JP7518755B2 - Electrically heated carrier and exhaust gas purification device - Google Patents

Description

The present invention relates to an electrically heated carrier. The present invention also relates to an exhaust gas purification device that uses an electrically heated carrier.

In recent years, electrically heated catalysts (EHCs) have been proposed to improve the deterioration of exhaust gas purification performance immediately after engine start. In EHCs, it is desirable to reduce temperature unevenness within the columnar honeycomb structure and achieve a uniform temperature distribution in order to fully obtain the catalytic effect.

In order to pass an electric current through the columnar honeycomb structure, it is necessary to electrically connect it to a terminal. Methods for joining the columnar honeycomb structure to a terminal include welding and brazing. However, terminals are generally made of metal, which is a different material from the ceramic columnar honeycomb structure. This poses the problem that cracks are likely to occur at the joint due to differences in thermal expansion. In applications where the structure is used in a high-temperature oxidizing atmosphere, such as inside an automobile exhaust pipe, it is necessary to ensure the mechanical and electrical joint reliability between the columnar honeycomb structure and the metal terminal in a high-temperature environment.

In response to this problem, Patent Document 1 (JP 2020-153366 A) proposes providing a weld base layer containing ceramics and metal between the metal terminal and the columnar honeycomb structure in order to mitigate the difference in thermal expansion between the ceramics constituting the columnar honeycomb structure and the metal terminal. The document also describes that the weld base layer containing 40 volume % or less of metal is connected to the metal terminal via a welded portion containing 40 volume % or more of metal.

JP 2020-153366 A

The columnar honeycomb structure of Patent Document 1 is an invention that aims to gradually increase the thermal expansion coefficient and suppress cracks by arranging multiple buffers that gradually increase the metal ratio from a columnar honeycomb structure made of conductive ceramics with a low thermal expansion coefficient toward a metal terminal with a high thermal expansion coefficient. However, changing the material type or material ratio used in the buffers changes the volume resistivity and specific heat. As a result, the rate of temperature increase when current is passed through the multiple buffers differs, and thermal stress occurs at the interface where the material ratio has been changed, which can lead to cracks. For this reason, there is still room for improvement in the reliability of the joint between the columnar honeycomb structure and the metal terminal.

The present invention was created in consideration of the above circumstances, and in one embodiment, it is an object of the present invention to provide an electrically heated carrier with improved bonding reliability between the metal terminal and the columnar honeycomb structure. In another embodiment, it is an object of the present invention to provide an exhaust gas purification device equipped with such an electrically heated carrier.

The above problems can be solved by the present invention, which is exemplified below.
[1]
An electrically conductive columnar honeycomb structure having an outer peripheral side surface and partition walls disposed inside the outer peripheral side surface and partitioning a plurality of cells forming a flow path from one end surface to the other end surface;
One or more base layers disposed directly or via an intermediate layer on the outer peripheral side surface of the honeycomb structure, and
a metal terminal bonded to the one or more substrate layers;
An electrically heated carrier comprising:
Each base layer is
a first underlayer in contact with the metal terminal, containing a metal and an oxide, the oxide being mainly composed of an amorphous oxide;
a second underlayer adjacent to the first underlayer and in contact with the outer peripheral side surface or the intermediate layer, containing a metal and an oxide, the oxide being mainly composed of a crystalline oxide;
Electrically heated carrier.
[2]
[1] An electrically heated carrier according to the present invention;
and a cylindrical metal tube that houses the electrically heated carrier.

According to one embodiment of the present invention, it is possible to provide an electrically heated carrier with improved bonding reliability between a metal terminal and a honeycomb structure. This electrically heated carrier can be used, for example, as a catalyst carrier for an exhaust gas purification device.

1 is a schematic diagram of an electrically heated carrier according to a first embodiment of the present invention, observed from one end face. FIG. FIG. 1 is a schematic perspective view of an electrically heated carrier according to a first embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a laminated structure of an outer wall, an electrode layer, a base layer, and a metal terminal for an electrically heated carrier according to a first embodiment of the present invention. FIG. FIG. 6 is a schematic diagram of an electrically heated carrier according to a second embodiment of the present invention, observed from one end face. FIG. 6 is a schematic perspective view of an electrically heated carrier according to a second embodiment of the present invention. 5 is a schematic cross-sectional view for explaining a laminated structure of an outer wall, an electrode layer, an intermediate layer, a base layer, and a metal terminal for an electrically heated carrier according to a second embodiment of the present invention. FIG.

Next, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

<Embodiment 1>
(1. Electrically Heated Carriers)
Fig. 1A is a schematic diagram of an electrically heated carrier 100 according to a first embodiment of the present invention when observed from one end surface 116. Fig. 1B is a schematic perspective view of the electrically heated carrier 100 according to the first embodiment of the present invention.
The electrically heated carrier 100 is
An electrically conductive columnar honeycomb structure 110 having an outer peripheral side surface 114 and partition walls 113 disposed inside the outer peripheral side surface 114 and defining a plurality of cells 115 that form flow paths from one end surface 116 to the other end surface 118;
one or more undercoat layers 120 disposed directly on the peripheral side surface 114 of the columnar honeycomb structure 110; and
A metal terminal 130 is provided bonded to one or more of the underlayers 120 .

By supporting a catalyst on the electrically heated carrier 100, the electrically heated carrier 100 can be used as a catalyst body. A fluid such as automobile exhaust gas can be flowed through the multiple cells 115. Examples of the catalyst include precious metal catalysts and other catalysts. Examples of the precious metal catalyst include three-way catalysts and oxidation catalysts in which precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the surface of alumina pores and contain co-catalysts such as ceria and zirconia, or NO _x storage reduction catalysts (LNT catalysts) containing alkaline earth metals and platinum as storage components for nitrogen oxides (NO _x ). Examples of catalysts that do not use precious metals include NO _x selective reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolite. In addition, two or more types of catalysts selected from these catalysts may be used. There is no particular restriction on the method of supporting the catalyst, and it can be performed in accordance with the conventional method of supporting a catalyst on a columnar honeycomb structure.

(1-1. Honeycomb structure)
The columnar honeycomb structure 110 has an outer peripheral side surface 114 and partition walls 113 disposed inside the outer peripheral side surface 114 and defining a plurality of cells 115 that form flow paths from one end surface 116 to the other end surface 118. The outer peripheral side surface 114 can be formed by the outer surface of the outer peripheral wall 112a. Furthermore, when an electrode layer 112b is disposed on the outer peripheral wall 112a, the outer peripheral side surface 114 can be formed by the outer surface of the electrode layer 112b.

The outer shape of the columnar honeycomb structure 110 is not particularly limited as long as it is columnar, and may be, for example, a columnar shape with a circular end face (cylindrical shape), a columnar shape with an oval end face, a columnar shape with a polygonal end face (quadragonal, pentagonal, hexagonal, heptagonal, octagonal, etc.), etc. In addition, the size of the columnar honeycomb structure 110 is preferably such that the area of one end face is 2000 to 20000 mm ² , more preferably 5000 to 15000 mm ² , for the reason of increasing heat resistance (suppressing cracks that extend in the circumferential direction of the outer peripheral side surface).

By disposing an electrode layer 112b having a lower volume resistivity than the outer peripheral wall 112a on the outer peripheral wall 112a, the current spreads easily in the circumferential direction of the columnar honeycomb structure 110 and in the extension direction of the cells 115, so that the uniform heat generation of the columnar honeycomb structure 110 can be improved. The electrode layer 112b may be disposed at one location on the outer surface of the outer peripheral wall 112a, or may be disposed at multiple locations. Therefore, in a preferred embodiment, a portion of the outer peripheral side surface 114 is constituted by a pair of electrode layers 112b disposed so as to face each other across the central axis of the columnar honeycomb structure 110. Specifically, in a cross section perpendicular to the cell 115, the angle θ (0°≦θ≦180°) between two line segments extending from the circumferential center of each of the pair of electrode layers 112b to the central axis O of the columnar honeycomb structure 110 is preferably 150°≦θ≦180°, more preferably 160°≦θ≦180°, even more preferably 170°≦θ≦180°, and most preferably 180°. However, the electrode layer 112b is not essential. Therefore, the outer peripheral side surface 114 may be composed of only the outer peripheral wall 112a without the electrode layer 112b.

Providing the outer peripheral wall 112a on the columnar honeycomb structure 110 is useful in terms of ensuring the structural strength of the columnar honeycomb structure 110 and suppressing leakage of the fluid flowing through the cells 115 from the outer peripheral side surface. In this respect, the thickness of the outer peripheral wall 112a is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.2 mm or more. However, if the outer peripheral wall 112a is made too thick, it will become too strong, and the strength balance with the partition wall 113 will be lost, resulting in a decrease in thermal shock resistance. Therefore, the thickness of the outer peripheral wall 112a is preferably 1.0 mm or less, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. Here, the thickness of the outer peripheral wall 112a is defined as the thickness in the normal direction to the tangent of the outer surface of the outer peripheral wall 112a at the measurement point when the portion of the outer peripheral wall 112a to be measured for thickness is observed in a cross section perpendicular to the extension direction of the cells 115.

There is no particular restriction on the formation area of the electrode layer 112b, but from the viewpoint of increasing the uniform heat generation of the columnar honeycomb structure 110, it is preferable that the electrode layer 112b is provided in a band shape extending in the circumferential direction of the columnar honeycomb structure 110 and the extension direction of the cell 115 on the outer surface of the outer wall 112a. Specifically, in a cross section perpendicular to the extension direction of the cell 115, the central angle α formed by two line segments connecting both side ends of each electrode layer 112b in the circumferential direction and the central axis O is preferably 30° or more, more preferably 40° or more, and even more preferably 60° or more, from the viewpoint of spreading the current in the circumferential direction and increasing the uniform heat generation. However, if the central angle α is made too large, the current passing through the inside of the columnar honeycomb structure 110 will be reduced, and the current passing near the outer wall 112a will be increased. Therefore, from the viewpoint of uniform heat generation of the columnar honeycomb structure 110, the central angle α is preferably 140° or less, more preferably 130° or less, and even more preferably 120° or less. In addition, it is desirable that each of the electrode layers 112b extends over 80% or more of the length between both end faces of the columnar honeycomb structure 110, preferably over 90% or more, and more preferably over the entire length. The electrode layer 112b may be composed of a single layer, or may have a laminated structure in which multiple layers are stacked.

The thickness of the electrode layer 112b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. By setting the thickness within this range, uniform heat generation can be improved. If the thickness of the electrode layer 112b is 0.01 mm or more, the electrical resistance can be appropriately controlled and more uniform heat generation can be achieved. If the thickness is 5 mm or less, the risk of breakage during canning is reduced. The thickness of the electrode layer 112b is defined as the thickness in the normal direction to the tangent of the outer surface of the electrode layer 112b at the measurement point when the part of the electrode layer 112b whose thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell 115.

By making the volume resistivity of the electrode layer 112b lower than the volume resistivity of the partition wall 113 and the outer peripheral wall 112a, electricity flows preferentially through the electrode layer 112b, and electricity spreads in the circumferential direction of the columnar honeycomb structure 110 and the extension direction of the cell 115 when current is applied. The volume resistivity of the electrode layer 112b is preferably 1/10 or less of the volume resistivity of the columnar honeycomb structure 110 and the outer peripheral wall 112a, more preferably 1/20 or less, and even more preferably 1/30 or less. However, if the difference in volume resistivity between the two becomes too large, current will concentrate between the ends of the opposing electrode layers 112b, causing the columnar honeycomb structure 110 to generate heat unevenly. Therefore, the volume resistivity of the electrode layer 112b is preferably 1/200 or more of the volume resistivity of the partition wall 113 and the outer peripheral wall 112a, more preferably 1/150 or more, and even more preferably 1/100 or more. In the present invention, the volume resistivity of the electrode layer, partition wall, and outer peripheral wall is a value measured at 25°C by the four-terminal method.

The material of the electrode layer 112b is not limited, but a composite material (cermet) of metal and ceramic (particularly conductive ceramic) can be used. Examples of metals include, for example, single metals such as Cr, Fe, Co, Ni, Si, or Ti, or alloys containing at least one metal selected from these metals. Examples of ceramics include, but are not limited to, silicon carbide (SiC), as well as metal compounds such as metal silicides such as tantalum silicide (TaSi ₂ ) and chromium silicide (CrSi ₂ ). Specific examples of composite materials (cermets) of metal and ceramics include composite materials of metal silicon and silicon carbide, composite materials of metal silicides such as tantalum silicide and chromium silicide, and composite materials in which one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride are added to one or more of the above metals from the viewpoint of reducing thermal expansion. As the material for the electrode layer 112b, among the various metals and ceramics mentioned above, a composite material of a metal silicide such as tantalum silicide or chromium silicide, metal silicon, and silicon carbide is preferred because it can be fired simultaneously with the partition wall and the outer peripheral wall, which contributes to simplifying the manufacturing process.

The outer peripheral wall 112a and the partition wall 113 have a higher volume resistivity than the electrode layer 112b, but are conductive. There are no particular limitations on the volume resistivity of the outer peripheral wall 112a and the partition wall 113 as long as they can generate heat by Joule heat when electricity is passed through them, but it is preferably 0.1 to 200 Ωcm, more preferably 1 to 200 Ωcm, and even more preferably 10 to 100 Ωcm.

The material of the outer peripheral wall 112a and the partition wall 113 is not particularly limited as long as it can generate heat by Joule heat when electricity is applied, and metals and ceramics (especially conductive ceramics) can be used alone or in combination. The material of the outer peripheral wall 112a and the partition wall 113 is not limited, but may contain one or more of oxide-based ceramics such as alumina, mullite, zirconia, and cordierite, and non-oxide-based ceramics such as silicon carbide, silicon nitride, and aluminum nitride. In addition, silicon carbide-metal silicon composite material, silicon carbide/graphite composite material, etc. can also be used. Among these, from the viewpoint of achieving both heat resistance and conductivity, the material of the outer peripheral wall 112a and the partition wall 113 is preferably a silicon-silicon carbide composite material or silicon carbide as the main component, and more preferably a silicon-silicon carbide composite material or silicon carbide. When the material of the outer peripheral wall 112a and the partition wall 113 is said to be mainly composed of silicon-silicon carbide composite, it means that the outer peripheral wall 112a and the partition wall 113 each contain 90% by mass or more of the silicon-silicon carbide composite (total mass). Here, the silicon-silicon carbide composite contains silicon carbide particles as aggregates and silicon as a binder that bonds the silicon carbide particles, and it is preferable that a plurality of silicon carbide particles are bonded by silicon so as to form pores between the silicon carbide particles. When the material of the outer peripheral wall 112a and the partition wall 113 is said to be mainly composed of silicon carbide, it means that the outer peripheral wall 112a and the partition wall 113 each contain 90% by mass or more of the silicon carbide (total mass).

When the outer peripheral wall 112a and the partition walls 113 contain a silicon-silicon carbide composite material, the ratio of the "mass of silicon as a binder" contained in the outer peripheral wall 112a and the partition walls 113 to the sum of the "mass of silicon carbide particles as aggregate" contained in the outer peripheral wall 112a and the partition walls 113 and the "mass of silicon as a binder" contained in the outer peripheral wall 112a and the partition walls 113 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%. If it is 10 mass% or more, the strength of the outer peripheral wall 112a and the partition walls 113 is sufficiently maintained. If it is 40 mass% or less, the shape is easily maintained during firing.

There are no limitations on the shape of the cells in a cross section perpendicular to the extension direction of the cells 115, but a square, hexagon, octagon, or a combination of these is preferable. Among these, a square and a hexagon are preferable. By using such a cell shape, the pressure loss when exhaust gas flows through the columnar honeycomb structure 110 is reduced, and the purification performance of the catalyst is excellent. From the viewpoint of easily achieving both structural strength and heating uniformity, a square shape is particularly preferable.

The cells 115 may extend from one end face 116 to the other end face 118. The cells 115 may be arranged alternately adjacent to each other with the partition wall 113 in between, with a first cell having one end face 116 plugged and the other end face 118 having an opening, and a second cell having one end face 116 opening and the other end face 118 plugged.

The thickness of the partition walls 113 that define the cells 115 is preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm. When the thickness of the partition walls 113 is 0.1 mm or more, it is possible to prevent the strength of the columnar honeycomb structure 110 from decreasing. When the thickness of the partition walls 113 is 0.3 mm or less, it is possible to prevent the pressure loss from increasing when exhaust gas is passed through the columnar honeycomb structure 110 when the columnar honeycomb structure 110 is used as a catalyst carrier to support a catalyst. In the present invention, the thickness of the partition walls 113 is defined as the length of the portion that passes through the partition walls 113 among the line segments connecting the centers of gravity of adjacent cells 115 in a cross section perpendicular to the extension direction of the cells 115.

The columnar honeycomb structure 110 preferably has a cell density of 40 to 150 cells/cm ² , more preferably 70 to 100 cells/cm ² , in a cross section perpendicular to the extension direction of the cells 115. By setting the cell density in such a range, it is possible to improve the purification performance of the catalyst while reducing the pressure loss when exhaust gas is made to flow through the columnar honeycomb structure 110. When the cell density is 40 cells/cm ² or more, a sufficient catalyst carrying area is ensured. When the cell density is 150 cells/cm ² or less, when the columnar honeycomb structure 110 is used as a catalyst carrier to carry a catalyst, it is possible to suppress the pressure loss from becoming too large when exhaust gas is made to flow. The cell density is a value obtained by dividing the number of cells by the area of one end face of the columnar honeycomb structure 110 excluding the outer wall 112 portion.

The partition walls 113 may be dense, such as in the form of Si-impregnated SiC, but are preferably porous. The porosity of the partition walls 113 is preferably 35-60%, and more preferably 35-45%. If the porosity is 35% or more, deformation during firing is more easily suppressed. If the porosity is 60% or less, the strength of the columnar honeycomb structure 110 is sufficiently maintained. The porosity is a value measured using a mercury porosimeter. Note that dense refers to a porosity of 5% or less.

The average pore diameter of the partition wall 113 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. If the average pore diameter is 2 μm or more, the volume resistivity is prevented from becoming too large. If the average pore diameter is 15 μm or less, the volume resistivity is prevented from becoming too small. The average pore diameter is a value measured by a mercury porosimeter.

(1-2. Base layer)
In the first embodiment, one or more base layers 120 are disposed directly on the outer peripheral side surface 114. When the columnar honeycomb structure 110 has an electrode layer 112b on the outer peripheral wall 112a, the base layer 120 is preferably disposed so as to contact the electrode layer 112b. On the other hand, when the columnar honeycomb structure 110 does not have an electrode layer 112b, the base layer 120 is disposed so as to contact the outer peripheral wall 112a.

There is no limit to the area and number of base layers 120 provided, but it is preferable to provide the area and number necessary for all metal terminals 130 to be bonded to the columnar honeycomb structure 110 via the base layers 120. In one embodiment, as shown in FIG. 1B, one bonding point with the metal terminal 130 can be formed on one base layer 120. Alternatively, multiple bonding points with the metal terminals 130 can be formed on one base layer 120.

FIG. 1C shows a schematic cross-sectional view for explaining the layered structure of the outer wall 112a, the electrode layer 112b, the base layer 120 and the metal terminal 130 of the electrically heated carrier 100 according to embodiment 1 of the present invention.
The underlayer 120 is
a first underlayer 120a in contact with the metal terminal 130, containing a metal and an oxide, the oxide being mainly composed of an amorphous oxide;
a second underlayer 120b adjacent to the first underlayer 120a and in contact with the outer peripheral wall 112a, containing a metal and an oxide, the oxide being mainly composed of a crystalline oxide;
The laminated structure includes:

While there is no substantial change in the volume resistivity and specific heat of oxides between the crystalline state and the amorphous state, the thermal expansion coefficient changes significantly. In general, amorphous oxides have a higher thermal expansion coefficient than crystalline oxides. For this reason, the first underlayer 120a, which contains a metal and an oxide and contains an amorphous oxide as the main component, contacts the metal terminal 130, and the second underlayer 120b, which contains a metal and an oxide and contains a crystalline oxide as the main component, is arranged so that the two are in contact with the outer wall 112a, so that the thermal expansion coefficient gradually decreases in the order of the metal terminal 130 → the first underlayer 120a → the second underlayer 120b → the outer wall 112a. This makes it possible to reduce the thermal expansion difference between the outer wall 112a of the columnar honeycomb structure and the metal terminal 130, and thus improve the bonding reliability between the outer wall 112a of the columnar honeycomb structure and the metal terminal 130. In this specification, unless otherwise specified, "thermal expansion coefficient" refers to the linear expansion coefficient measured according to JIS Z2285:2003 when changing from 25°C to 1000°C.

In one embodiment, the linear expansion coefficient _α1 of the first underlayer 120a and the linear expansion coefficient α2 of the second underlayer 120b can satisfy the relationship 3.0≧ _α1 / _α2 ≧1.2, as measured according to JIS Z2285:2003 when the temperature is changed from 25° C. to 1000° C. However, since an excessively large _α1 / _α2 may cause cracks to occur at the boundary between the first underlayer 120a and the second underlayer 120b, the linear expansion coefficient α1 of the _first underlayer 120a and the linear expansion coefficient α2 of the second underlayer 120b preferably satisfy the relationship 2.0≧ _α1 / _α2 ≧1.2, and more preferably satisfy the relationship 1.7≧ _α1 / _α2 ≧1.2.

In one embodiment, the linear expansion coefficient _α2 of the second underlayer 120b and the linear expansion coefficient α3 of the member (the outer peripheral wall 112a or the electrode layer 112b) constituting the outer peripheral side surface with which the second underlayer 120b comes into contact can satisfy the relationship 2.0 ≧ _α2 / _α3 ≧ 1.0, as measured according to JIS Z2285: ₂₀₀₃ when the temperature is changed from 25°C to 1000°C. However, since an excessively large _α2 / _α3 may cause cracks to occur at the boundary between the second underlayer 120b and the outer peripheral wall 112a, the relationship 2.0 ≧ _α2 / _α3 ≧ 1.2 is preferably satisfied, and the relationship 2.0 ≧ _α2 / _α3 ≧ 1.3 is more preferably satisfied.

The first underlayer 120a and the second underlayer 120b may each contain both crystalline oxide and amorphous oxide, but the first underlayer 120a contains an amorphous oxide as the main component of the oxide, and the second underlayer 120b contains a crystalline oxide as the main component of the oxide. The main component of the oxide means a component that occupies more than 50 volume % of the oxide, and is preferably 70 volume % or more.

The volume ratio of crystalline oxide and the volume ratio of amorphous oxide in the oxide in the first underlayer 120a and the second underlayer 120b can be measured by the following method. The underlayer 120 is cut in the thickness direction along a cutting line that passes through the center of gravity of the joint portion, typically the welded portion 131, and is parallel to the extension direction of the cell 115, and an SEM image of the underlayer cross section is obtained. The brightest area on the SEM image is determined to have a brightness of 100%, the darkest area is determined to have a brightness of 0%, and areas with a brightness of 90% or more are determined to be metal and areas with a brightness of 10% or less are determined to be voids, so that the parts of the SEM image excluding the metal parts and voids are regarded as oxides. In the SEM image in which the oxide area is identified, the relatively light colored areas are determined to be amorphous oxides and the relatively dark colored areas are determined to be crystalline oxides according to the shade of the image. The area ratios of the determined amorphous oxide and crystalline oxide are regarded as volume ratios, and the volume ratios of the amorphous oxide and the crystalline oxide in the oxide are calculated. In addition to the method of distinguishing the oxide regions by the shading of the SEM images, it is also possible to calculate the area ratios of the crystalline and amorphous regions by observing the crystal phase distribution using the EBSD method on the cross section of the base layer.

The first underlayer 120a and the second underlayer 120b preferably have a small difference in volume resistivity while having a difference in thermal expansion coefficient. According to an embodiment of the present invention, the volume resistivity _ρ1 of the first underlayer 120a and the volume resistivity _ρ2 of the second underlayer 120b can satisfy the relationship of 1.0≦ _ρ1 / _ρ2 ≦1.5, as measured by a four-terminal method, and preferably satisfy the relationship of 1.0≦ _ρ1 / _ρ2 ≦1.3, and more preferably satisfy the relationship of 1.0≦ _ρ1 / _ρ2 ≦1.1.

The amorphous oxide contained in the first underlayer 120a and the crystalline oxide contained in the second underlayer 120b may be oxides of elements with the same atomic number, or oxides with different atomic numbers. However, from the viewpoint of reducing the difference in volume resistivity and specific heat in the first underlayer 120a and the second underlayer 120b to further suppress crack generation, it is preferable to use oxides with a small difference in volume resistivity and specific heat for the oxides used in the first underlayer 120a and the second underlayer 120b. For this reason, it is preferable that the first underlayer 120a contains one or more amorphous oxides selected from oxide glass and chalcogenide glass, and the second underlayer 120b contains one or more crystalline oxides selected from oxide glass and chalcogenide glass. Examples of oxide glass include borosilicate glass, aluminosilicate glass, and soda-lime glass. Examples of chalcogenide glass include Cu-Sb-S glass, Ge-As-Se glass, and _GeO2 - _GeS2 glass. In a more preferred embodiment, the amorphous oxide contained in the first underlayer 120a and the crystalline oxide contained in the second underlayer 120b are oxides of elements having the same atomic number. Oxides of the same element are more preferred because they have substantially the same volume resistivity and specific heat.

The first underlayer 120a and the second underlayer 120b each preferably contain one or more metals selected from, but not limited to, a Ni-based alloy, an Fe-based alloy, a Ti-based alloy, a Co-based alloy, metallic silicon, and Cr. More preferably, they are composed of a Ni-based alloy, an Fe-based alloy, a Ti-based alloy, or a Co-based alloy. This is due to oxidation resistance. Examples of Ni-based alloys include Inconel and Hastelloy. Examples of Fe-based alloys include stainless steel such as SUS430. Examples of Ti-based alloys include JIS 60 (ASTM B348 Gr5). Examples of Co-based alloys include Stellite. Among these, Fe-based alloys (e.g., ferritic stainless steel) are preferred because of the small difference in thermal expansion coefficient with the columnar honeycomb structure. The atomic numbers of the metals contained in the first underlayer 120a and the second underlayer 120b may be the same or different. However, in order to reduce the difference in thermal expansion coefficient between the underlayers, it is preferable that both the first underlayer 120a and the second underlayer 120b contain metals with the same atomic number.

In a preferred embodiment, the first underlayer 120a is made of an Fe-based alloy and amorphous oxide glass, and the second underlayer 120b is made of an Fe-based alloy and crystalline oxide glass. Examples of oxide glass include borosilicate glass, aluminosilicate glass, and soda-lime glass. Examples of aluminosilicate glass include Mg-Al-Si oxides. A suitable combination of an Fe-based alloy and amorphous/crystalline oxide glass is, for example, a combination of stainless steel such as SUS430 and an Mg-Al-Si oxide (e.g., MgO-Al ₂ O ₃ -SiO ₂ ).

From the viewpoint of reducing the difference between the volume resistivity and the specific heat in the first underlayer 120a and the second underlayer 120b and further suppressing the occurrence of cracks, it is desirable that the difference between the volume concentration of the metal in the first underlayer 120a and the volume concentration of the metal in the second underlayer 120b is small. Thus, in a preferred embodiment, the volume concentration _v1 (%) of the metal in the first underlayer 120a and the volume concentration _v2 (%) of the metal in the second underlayer 120b satisfy the relationship 0.7≦ _v1 / _v2 ≦1.6. It is more preferable that the relationship 0.8≦ _v1 / _v2 ≦1.4 is satisfied, and it is even more preferable that the relationship 0.9≦ _v1 / _v2 ≦1.2 is satisfied.

The volume concentration (v ₁ , v ₂ ) of the metal in the first underlayer 120a and the second underlayer 120b is not particularly limited, but may be, for example, in the range of 20 volume % to 80 volume %, typically in the range of 30 volume % to 70 volume %. The volume concentration of the metal in the underlayer is determined by cutting the underlayer 120 in the thickness direction along a cutting line that passes through the center of gravity of the welded portion 131 and is parallel to the extension direction of the cell 115, obtaining an SEM image of the underlayer cross section using a scanning electron microscope (SEM), binarizing the SEM image to separate it into metal and other parts (mainly oxides and voids), and the area ratio of the metal on the SEM image is determined as the volume concentration of the metal. The binarization is performed using a threshold designation method. The brightest area on the SEM image is defined as 100% bright, the darkest area as 0% bright, and areas with a brightness of 90% or more are considered to be metal.

The thickness of the first underlayer 120a at the point in contact with the metal terminal 130 is preferably 0.1 to 0.5 mm, and more preferably 0.3 to 0.5 mm. If the thickness of the first underlayer 120a at the point in contact with the metal terminal 130 is 0.1 mm or more, the advantage of stable adhesion strength during bonding is obtained. If the thickness of the first underlayer 120a at the point in contact with the metal terminal 130 is 0.5 mm or less, the advantage of suppressing stress between the first underlayer 120a and the metal terminal is obtained. The thickness of the first underlayer 120a at the point in contact with the metal terminal 130 is defined as the thickness in the normal direction to the tangent of the outer surface of the first underlayer 120a at the measurement point when the first underlayer 120a whose thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell.

The thickness of the second underlayer 120b at the location adjacent to the first underlayer 120a is preferably 0.2 to 1.0 mm, and more preferably 0.4 to 0.6 mm. If the thickness of the second underlayer 120b at the location adjacent to the first underlayer 120a is 0.2 mm or more, the advantage of being able to suppress the stress between the honeycomb structure and the first underlayer is obtained. If the thickness of the second underlayer 120b at the location adjacent to the first underlayer 120a is 1.0 mm or less, the advantage of being able to reduce the voltage drop in the underlayer is obtained. The thickness of the second underlayer 120b at the location adjacent to the first underlayer 120a is defined as the thickness in the normal direction to the tangent of the outer surface of the second underlayer 120b at the measurement location when the second underlayer 120b whose thickness is to be measured is observed at a cross section perpendicular to the extension direction of the cell.

(1-3. Metal terminal)
The metal terminal 130 is joined to one or more base layers 120. When a voltage is applied to the columnar honeycomb structure 110 via the metal terminal 130, electricity flows and the columnar honeycomb structure 110 generates heat by Joule heat. Therefore, the columnar honeycomb structure 110 can be suitably used as a heater. In a preferred embodiment, the columnar honeycomb structure 110 has a peripheral wall 112a on which a central axis of the columnar honeycomb structure 110 is aligned. The semiconductor device has a pair of electrode layers 112b disposed so as to sandwich and face each other, and one or more metal terminals 130 are bonded to each electrode layer 112b via a base layer 120. This makes it possible to improve the uniform heat generation property of the columnar honeycomb structure 110. The applied voltage is preferably 12 to 900 V, and more preferably 48 to 600 V, but the applied voltage can be changed appropriately.

The method of joining the metal terminal 130 and the underlayer 120 is not particularly limited, but examples include welding and brazing. Among them, welding is preferred, and laser welding is more preferred, because there is little deterioration of the joint area even when heated to 800°C or higher. Therefore, in a preferred embodiment, the metal terminal 130 has a welded area 131 that is joined to the underlayer 120.

There are no particular restrictions on the material of the metal terminal 130 so long as it is a metal, and simple metals and alloys can be used, but from the standpoint of corrosion resistance, volume resistivity, and linear expansion coefficient, it is preferable to use an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni, and Ti, and stainless steel and Fe-Ni alloys are more preferable. The shape and size of the metal terminal 130 are not particularly limited, and can be designed appropriately depending on the size and electrical conductivity of the columnar honeycomb structure 110, etc.

One metal terminal 130 can be joined to the electrode layer 112b via one or more welded portions 131. It is preferable to reduce the welded area of each welded portion 131 in order to suppress cracking and peeling due to thermal expansion differences. Specifically, the welded area of each welded portion 131 is preferably 50 mm ² or less, more preferably 45 mm ² or less, even more preferably 40 mm ² or less, and even more preferably 30 mm ² or less. However, if the welded area of each welded portion 131 is too small, the joining strength cannot be ensured, so it is preferably 2 mm ² or more, more preferably 3 mm ² or more, and even more preferably 4 mm ² or more.

(2. Manufacturing Method)
Next, a method for manufacturing the electrically heated carrier according to the embodiment 1 will be described by way of example. The electrically heated carrier according to the embodiment 1 can be manufactured by a manufacturing method including a process A1 for obtaining a columnar honeycomb molded body, a process A2 for obtaining an unfired columnar honeycomb structure with an electrode layer forming paste, a process A3 for obtaining a columnar honeycomb structure by firing the unfired columnar honeycomb structure with an electrode layer forming paste, a process A4 for applying a base layer forming paste onto the electrode layer of the columnar honeycomb structure to obtain a columnar honeycomb structure with a base layer forming paste, a process A5 for performing a firing process on the columnar honeycomb structure with the base layer forming paste to obtain a columnar honeycomb structure with a second base layer, a process A6 for changing the surface layer portion of the second base layer into a first base layer, and a process A7 for joining a metal terminal to the base layer.

(Step A1)
Step A1 is a step of preparing a columnar honeycomb molded body, which is a precursor of the columnar honeycomb structure. The columnar honeycomb molded body can be prepared according to a method for preparing a columnar honeycomb molded body in a known method for manufacturing a columnar honeycomb structure. For example, first, a forming raw material is prepared by adding metal silicon powder (metal silicon), a binder, a surfactant, a pore former, water, etc. to silicon carbide powder (silicon carbide). It is preferable that the mass of the metal silicon powder is 10 to 40 mass% with respect to the total mass of the silicon carbide powder and the metal silicon powder. The average particle diameter of the silicon carbide particles in the silicon carbide powder is preferably 3 to 50 μm, more preferably 3 to 40 μm. The average particle diameter of the metal silicon particles in the metal silicon powder is preferably 2 to 35 μm. The average particle diameter of the silicon carbide particles and the metal silicon particles refers to the arithmetic mean diameter based on the volume when the frequency distribution of the particle size is measured by a laser diffraction method. The silicon carbide particles are fine particles of silicon carbide that constitute silicon carbide powder, and the metallic silicon particles are fine particles of metallic silicon that constitute metallic silicon powder. Note that this is the blending of the forming raw materials when the material of the honeycomb structure is a silicon-silicon carbide composite material, and when the material of the honeycomb structure is silicon carbide, metallic silicon is not added.

Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the binder is preferably 2.0 to 10.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

Surfactants that can be used include ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc. These may be used alone or in combination of two or more. The content of the surfactant is preferably 0.1 to 2.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

The pore-forming material is not particularly limited as long as it forms pores after firing, and examples include graphite, starch, foamed resin, water-absorbent resin, silica gel, etc. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass. The average particle diameter of the pore-forming material is preferably 10 to 30 μm. The average particle diameter of the pore-forming material refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by the laser diffraction method. When the pore-forming material is a water-absorbent resin, the average particle diameter of the pore-forming material refers to the average particle diameter after absorbing water.

The water content is preferably 20 to 60 parts by mass when the total mass of the silicon carbide powder and the silicon metal powder is 100 parts by mass.

Next, the obtained forming raw materials are kneaded to form a clay, and the clay is then extruded to produce a columnar honeycomb formed body having an outer peripheral wall and partition walls. A die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used during extrusion molding. Next, it is preferable to dry the obtained columnar honeycomb formed body. If the length of the columnar honeycomb formed body in the central axis direction is not the desired length, both ends of the honeycomb formed body can be cut to the desired length. The columnar honeycomb formed body after drying is called a columnar honeycomb dried body.

As a variation of step A1, the columnar honeycomb formed body may be fired once. That is, in this variation, the columnar honeycomb formed body is fired to produce a columnar honeycomb fired body, and step A2 is then carried out on the columnar honeycomb fired body.

(Step A2)
Step A2 is a step of applying an electrode layer forming paste to the side surface of the columnar honeycomb molded body to obtain an unfired columnar honeycomb structure with an electrode layer forming paste. The electrode layer forming paste can be formed by appropriately adding various additives to raw material powders (metal powders, ceramic powders, etc.) mixed according to the required characteristics of the electrode layer, and kneading the mixture. The average particle diameter of the raw material powder is not limited, but is preferably, for example, 5 to 50 μm, and more preferably 10 to 30 μm. The average particle diameter of the raw material powder refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by a laser diffraction method.

Next, the obtained electrode layer forming paste is applied to the required locations on the side of a columnar honeycomb formed body (typically a dried columnar honeycomb body) to obtain an unfired columnar honeycomb structure with electrode layer forming paste. The method of preparing the electrode layer forming paste and the method of applying the electrode layer forming paste to the columnar honeycomb formed body can be performed in accordance with known manufacturing methods for honeycomb structures, but in order to give the electrode layer a lower volume resistivity than the outer peripheral wall and partition walls, the metal content can be made higher than that of the outer peripheral wall and partition walls, or the particle size of the metal particles in the raw material powder can be made smaller.

(Step A3)
Step A3 is a step of obtaining a columnar honeycomb structure by firing the unfired columnar honeycomb structure with the electrode layer forming paste. Before firing, the unfired columnar honeycomb structure with the electrode layer forming paste may be dried. Also, before firing, degreasing may be performed to remove binders and the like. As firing conditions, depending on the material of the columnar honeycomb structure, it is preferable to heat at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. Also, after firing, it is preferable to perform oxidation treatment at 1200 to 1350°C for 1 to 10 hours in order to improve durability. The method of degreasing and firing is not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

(Step A4)
Step A4 is a step of applying a base layer forming paste onto the electrode layer of the columnar honeycomb structure to obtain a columnar honeycomb structure with a base layer forming paste. The base layer forming paste can be formed by appropriately adding various additives to raw material powders (metal powders, oxide powders, etc.) mixed according to the required characteristics of the base layer and kneading them. It is preferable to use a crystalline oxide powder as the oxide powder. Examples of the crystalline oxide powder include, but are not limited to, crystalline oxide glass, crystalline Si-based materials, and crystalline chalcogenide materials. Crystalline oxide glass is preferable. The average particle size of the raw material powder is, but is not limited to, preferably 2 to 40 μm, and more preferably 5 to 20 μm. The average particle size of the raw material powder refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by a laser diffraction method.

As the underlayer forming paste, it is sufficient to prepare one type of paste, instead of preparing a first underlayer forming paste and a second underlayer forming paste separately. As described later, this is because a laminated structure can be constructed by changing a crystalline oxide into an amorphous oxide by heat treatment. However, as the underlayer forming paste, the first underlayer forming paste and the second underlayer forming paste may be prepared separately.

(Step A5)
Step A5 is a step of performing a firing process on the columnar honeycomb structure with the underlayer forming paste to obtain a columnar honeycomb structure with a second underlayer. As firing conditions, depending on the material of the underlayer, it is preferable to heat in an inert atmosphere such as nitrogen or argon at a temperature at which the crystalline oxide does not change to an amorphous oxide. For example, when a crystalline oxide glass is used as the crystalline oxide, it changes to an amorphous state at around 1200°C, so it is desirable to fire at a temperature lower than that, and for example, it is preferable to perform a firing process at 1000 to 1150°C for 2 to 6 hours. The firing method is not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

(Step A6)
Step A6 is a step of changing the surface portion of the second underlayer into the first underlayer. Illustratively, by irradiating the outer surface of the second underlayer with a laser, the crystalline oxide contained in the second underlayer can be changed into an amorphous oxide to form the first underlayer. In addition, by irradiating the laser, the material is rapidly cooled after heating, so that recrystallization can be suppressed and the material can exist in the form of an amorphous oxide. The thickness of the first underlayer can be controlled by the output and time of the laser irradiation. The laser irradiation is performed under conditions where the surface portion of the second underlayer reaches a temperature at which the crystalline oxide contained in the second underlayer can be changed into an amorphous oxide. For example, when the second underlayer contains a crystalline oxide glass as a crystalline oxide, it changes into an amorphous state at around 1200°C, so it is necessary to irradiate the laser under conditions where the temperature reaches a higher temperature, for example, in the range of 1200 to 1500°C. However, when the second underlayer is irradiated with a laser and becomes extremely hot, the metal components may melt and aggregate, or the oxide components may be blown away by inert gas such as Ar gas supplied for oxidation prevention during laser irradiation. For example, when the second underlayer contains SUS430 as a metal component, it melts at about 1500°C or higher. When it contains crystalline oxide glass as a crystalline oxide, the oxide is partially blown away at about 1400°C or higher. In this case, the volume concentration of the metal in the first underlayer increases, and a difference occurs between the volume concentration of the metal in the second underlayer. Therefore, it is desirable to suppress excessive temperature rise of the second underlayer by repeatedly irradiating a laser with a small spot diameter at multiple locations for a short time with high output. For example, the spot diameter can be 0.1 to 0.3 mm, the laser output can be 50 to 200 W/mm ² , and the laser irradiation time for one time can be 0.1 to 1.5 seconds, more preferably 0.75 to 1.5 seconds. After one laser irradiation is completed, it is preferable to allow the temperature of the irradiated portion to cool sufficiently before performing the next laser irradiation.

(Step A7)
Step A7 is a step of joining a metal terminal to the underlayer. There are no particular limitations on the joining method, such as welding and brazing, but laser welding is preferred from the viewpoint of controlling the welding area and production efficiency. As a method of laser welding, a method of welding the metal terminal to the first underlayer by irradiating a laser from the metal terminal side with a metal terminal placed on the outer surface of the first underlayer is exemplified. If the laser output during laser welding is too high, a hole will be made in the metal terminal, and if it is too low, joining will not be possible. Therefore, it is preferable to adjust the laser output so that the temperature is such that the underlayer melts at an output that does not melt the metal too much. Depending on the material and thickness of the metal terminal, the laser output during laser welding can be, for example, 50 to 300 W/mm ² .

The above is an exemplary explanation of the manufacturing method of an electrically heated carrier according to embodiment 1 in the case where an electrode layer is disposed on the outer wall of the columnar honeycomb structure. In the case where an electrode layer is not disposed on the outer wall of the columnar honeycomb structure, a columnar honeycomb structure in which the electrode layer forming process is omitted is obtained, and a base layer forming paste is applied to the outer wall of the columnar honeycomb structure to obtain a columnar honeycomb structure with a base layer forming paste. The subsequent processes are as described above.

(3. Exhaust Gas Purification Device)
The electrically heated carrier 100 according to the first embodiment can be used in an exhaust gas purification device. The exhaust gas purification device has an electrically heated carrier and a cylindrical metal tube that houses the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier can be installed in the middle of an exhaust gas flow path for passing exhaust gas from an engine. As the metal tube, a metallic cylindrical member that houses the electrically heated carrier can be used.

<Embodiment 2>
(1. Electrically Heated Carriers)
FIG. 2A is a schematic diagram of an electrically heated carrier 200 according to a second embodiment of the present invention when observed from one end surface 116. FIG. 2B is a schematic perspective view of an electrically heated carrier 200 according to a second embodiment of the present invention. FIG. 2C is a schematic cross-sectional view for explaining a laminated structure of an outer peripheral wall 112a, an electrode layer 112b, an intermediate layer 140, a base layer 120, and a metal terminal 130 for an electrically heated carrier 200 according to a second embodiment of the present invention. In FIG. 2A to FIG. 2C, components given the same reference numerals as those shown in FIG. 1A to FIG. 1C are as described in the description of the electrically heated carrier 100 according to the first embodiment, and the description of the embodiment is also overlapped, so that the description will be omitted unless otherwise specified.

The difference between embodiment 2 and embodiment 1 is that in embodiment 1, one or more base layers 120 are arranged directly on the peripheral side surface 114 of the columnar honeycomb structure 110, whereas in embodiment 2, one or more base layers 120 are arranged on the peripheral side surface 114 of the columnar honeycomb structure 110 via an intermediate layer 140.
Therefore, the electrically heated carrier 200 is
An electrically conductive columnar honeycomb structure 110 having an outer peripheral side surface 114 and partition walls 113 disposed inside the outer peripheral side surface 114 and defining a plurality of cells 115 that form flow paths from one end surface 116 to the other end surface 118;
One or more base layers 120 disposed on the outer peripheral side surface 114 of the columnar honeycomb structure 110 via an intermediate layer 140; and
A metal terminal 130 is provided bonded to one or more of the underlayers 120 .

In embodiment 2, one or more base layers 120 are disposed on the outer peripheral side surface 114 via an intermediate layer 140. When the columnar honeycomb structure 110 has an electrode layer 112b, the intermediate layer 140 is preferably disposed so as to contact the electrode layer 112b. On the other hand, when the columnar honeycomb structure 110 does not have an electrode layer 112b, the intermediate layer 140 is disposed so as to contact the outer peripheral wall 112a.

There is no limit to the area and number of intermediate layers 140 provided, but it is preferable to provide the area and number necessary for all base layers 120 to be bonded to the columnar honeycomb structure 110 via the intermediate layers 140. In one embodiment, as shown in FIG. 2B, one base layer 120 can be formed on one intermediate layer 140. Alternatively, multiple base layers 120 may be formed on one intermediate layer 140. One intermediate layer 140 may be composed of a single layer, or may have a layered structure in which multiple layers are stacked.

Figure 2C shows a schematic cross-sectional view for explaining the layered structure of the outer wall 112a, electrode layer 112b, intermediate layer 140, base layer 120 and metal terminal 130 of the electrically heated carrier 200 according to embodiment 2 of the present invention.
The underlayer 120 is
a first underlayer 120a in contact with the metal terminal 130, containing a metal and an oxide, the oxide being mainly composed of an amorphous oxide;
a second underlayer 120b in contact with the first underlayer 120a and the intermediate layer 140, containing a metal and an oxide, the oxide being mainly composed of a crystalline oxide;
The laminated structure includes:

By disposing the intermediate layer 140 between the outer peripheral wall 112a or the electrode layer 112b and the underlayer 120, it is possible to suppress unexpected reactions between the outer peripheral wall 112a or the electrode layer 112b and the underlayer 120, which may cause changes in thermal expansion or a decrease in strength. In particular, when the outer peripheral wall 112a, the electrode layer 112b, or the underlayer 120 contains silicon, it is possible to suppress the generation of silicides and a decrease in strength. It is preferable to gradually decrease the thermal expansion coefficient in the order of the metal terminal 130 → the first underlayer 120a → the second underlayer 120b → the intermediate layer 140 → (the electrode layer 112b) → the outer peripheral wall 112a. This makes it possible to reduce the thermal expansion difference between the outer wall 112a or electrode layer 112b of the columnar honeycomb structure 110 and the metal terminal 130, thereby improving the bonding reliability between the outer wall 112a or electrode layer 112b of the columnar honeycomb structure 110 and the metal terminal 130.

The intermediate layer 140 preferably contains, but is not limited to, a silicon compound (glass) and/or cordierite. Among these, it is preferable that the intermediate layer 140 contains an amorphous silicon compound.

The thickness of the intermediate layer 140 at the point where it contacts the second underlayer 120b is preferably 0.1 to 0.5 mm, and more preferably 0.1 to 0.3 mm. If the thickness of the intermediate layer 140 at the point where it contacts the second underlayer 120b is 0.1 mm or more, the advantage of significantly suppressing the generation of silicides is obtained. If the thickness of the intermediate layer 140 at the point where it contacts the second underlayer 120b is 0.5 mm or less, the advantage of significantly suppressing the voltage drop in the intermediate layer 140 is obtained. The thickness of the intermediate layer 140 at the point where it contacts the second underlayer 120b is defined as the thickness in the normal direction to the tangent of the outer surface of the intermediate layer 140 at the measurement point when the point of the intermediate layer 140 where the thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell.

In one embodiment, the linear expansion coefficient _α2 of the second underlayer 120b and the linear expansion coefficient _α3 of the intermediate layer 140 with which the second underlayer 120b is in contact can satisfy the relationship 2.0≧ _α2 / _α3 ≧1.0, as measured according to JIS Z2285:2003 when the temperature is changed from 25° C. to 1000° C. However, since an excessively large _α2 / _α3 may cause cracks to occur at the boundary between the second underlayer 120b and the intermediate layer 140, the relationship preferably satisfies 1.8≧ _α2 / _α3 ≧1.0, and more preferably satisfies 1.6≧ _α2 / _α3 ≧1.0.

(2. Manufacturing Method)
Next, a method for producing the electrically heated carrier according to the second embodiment will be described by way of example. The electrically heated carrier of embodiment 2 can be manufactured by a manufacturing method including a step A1 of obtaining a columnar honeycomb formed body, a step A2 of obtaining an unfired columnar honeycomb structure with an electrode layer forming paste, a step A3 of firing the unfired columnar honeycomb structure with the electrode layer forming paste to obtain a columnar honeycomb structure, a step A4-1 of applying an intermediate layer forming paste onto the electrode layer of the columnar honeycomb structure to obtain a columnar honeycomb structure with the intermediate layer forming paste, a step A4-2 of applying a base layer forming paste onto the intermediate layer forming paste of the columnar honeycomb structure with the intermediate layer forming paste to obtain a columnar honeycomb structure with the base layer forming paste, a step A5 of firing the columnar honeycomb structure with the base layer forming paste to obtain a columnar honeycomb structure with a second base layer, a step A6 of changing the surface portion of the second base layer into a first base layer, and a step A7 of joining a metal terminal to the base layer.

(Step A1 to Step A3)
Steps A1 to A3 are the same as those described in the method for producing the electrically heated carrier 100 according to the first embodiment.

(Step A4-1)
Step A4-1 is a step of applying an intermediate layer forming paste onto the electrode layer of the columnar honeycomb structure to obtain a columnar honeycomb structure with an intermediate layer forming paste. The intermediate layer forming paste can be formed by appropriately adding various additives to raw material powder (silicon compound powder, etc.) blended according to the required characteristics of the intermediate layer, and kneading the mixture. The average particle size of the raw material powder is not limited, but is preferably, for example, 1 to 10 μm, and more preferably 2 to 5 μm. The average particle size of the raw material powder refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by a laser diffraction method. After application, the intermediate layer forming paste is preferably dried.

(Step A4-2)
Step A4-2 is a step of applying a base layer forming paste onto the intermediate layer forming paste of the columnar honeycomb structure with the intermediate layer forming paste to obtain a columnar honeycomb structure with the base layer forming paste. The base layer forming paste can be formed by appropriately adding various additives to raw material powders (metal powders, oxide powders, etc.) mixed according to the required characteristics of the base layer and kneading them. It is preferable to use a crystalline oxide powder as the oxide powder. Examples of the crystalline oxide powder include, but are not limited to, crystalline oxide glass and crystalline chalcogenide materials. Crystalline oxide glass is preferable. However, it is also possible to prepare a base layer forming paste using an amorphous oxide powder, and heat it after application to crystallize it. The average particle size of the raw material powder is, but is not limited to, preferably 2 to 40 μm, and more preferably 5 to 20 μm. The average particle size of the raw material powder refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by a laser diffraction method.

(Step A5)
Step A5 is a step of performing a firing process on the columnar honeycomb structure with the underlayer forming paste to obtain a columnar honeycomb structure with a second underlayer. In this step, the intermediate layer and the underlayer are formed by firing. As for the firing conditions, depending on the material of the underlayer, it is preferable to heat in an inert atmosphere such as nitrogen or argon at a temperature at which the crystalline oxide does not change to an amorphous oxide. For example, when a crystalline oxide glass is used as the crystalline oxide, it changes to an amorphous state at around 1200°C, so it is desirable to fire at a temperature lower than that, and for example, it is preferable to perform a firing process at 1000 to 1150°C for 2 to 6 hours. The firing method is not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

(Step A6 to Step A7)
Steps A6 to A7 are the same as those described in the method for producing the electrically heated carrier 100 according to the first embodiment.

The above describes the manufacturing method of an electrically heated carrier according to embodiment 2 in which an electrode layer is disposed on the outer wall of the columnar honeycomb structure. In cases in which an electrode layer is not disposed on the outer wall of the columnar honeycomb structure, a columnar honeycomb structure in which the electrode layer forming process is omitted can be obtained, and an intermediate layer forming paste can be applied to the outer wall of the columnar honeycomb structure to obtain a columnar honeycomb structure with intermediate layer forming paste. The subsequent steps are as described above.

(3. Exhaust Gas Purification Device)
The electrically heated carrier 200 according to the second embodiment can be used in an exhaust gas purification device. The exhaust gas purification device has an electrically heated carrier and a cylindrical metal tube that houses the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier can be installed in the middle of an exhaust gas flow path for passing exhaust gas from an engine. As the metal tube, a metallic cylindrical member that houses the electrically heated carrier can be used.

The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

<I. Comparative Examples 1-2, Invention Examples 1-5>
(1. Preparation of cylindrical clay)
A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and metal silicon (Si) powder in a mass ratio of 80:20. Hydroxypropyl methylcellulose was added as a binder and a water-absorbent resin was added as a pore-forming material to the ceramic raw material, and water was added to prepare a molding raw material. The molding raw material was kneaded by a vacuum clay kneader to prepare a cylindrical clay. The binder content was 7 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The pore-forming material content was 3 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The water content was 42 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The average particle diameter of the silicon carbide powder was 20 μm, and the average particle diameter of the metal silicon powder was 6 μm. The average particle size of the pore-forming material was 20 μm. The average particle sizes of the silicon carbide powder, the metallic silicon powder and the pore-forming material refer to arithmetic mean diameters based on volume when the frequency distribution of particle sizes is measured by a laser diffraction method.

(2. Preparation of dried honeycomb body)
The obtained cylindrical clay was molded using an extrusion molding machine with a checkerboard die structure to obtain a cylindrical honeycomb molded body in which each cell shape in a cross section perpendicular to the flow direction of the cells is a square. This honeycomb molded body was dried by high-frequency dielectric heating, and then dried at 120°C for 2 hours using a hot air dryer, and both bottom surfaces were cut by a predetermined amount to produce a columnar honeycomb dried body.

(3. Preparation of electrode layer forming paste)
Metallic silicon (Si) powder, silicon carbide (SiC) powder, methyl cellulose, glycerin, and water were mixed with a rotation and revolution mixer to prepare an electrode layer forming paste. The Si powder and the SiC powder were mixed so that the volume ratio of the Si powder:SiC powder was 40:60. In addition, when the total of the Si powder and the SiC powder was 100 parts by mass, the methyl cellulose was 0.5 parts by mass, the glycerin was 10 parts by mass, and the water was 38 parts by mass. The average particle diameter of the metallic silicon powder was 6 μm. The average particle diameter of the silicon carbide powder was 35 μm. These average particle diameters refer to the arithmetic mean diameter based on the volume when the frequency distribution of the particle size was measured by the laser diffraction method.

(4. Application of electrode layer forming paste)
The electrode layer forming paste was applied to two locations on the outer surface of the outer peripheral wall of the columnar honeycomb dried body by a curved surface printing machine so as to face each other across the central axis. Each application portion was formed in a band shape over the entire length between both bottom surfaces of the honeycomb dried body (angle θ = 180°, central angle α = 90°).

(5. Firing)
The columnar honeycomb structure with the electrode layer forming paste was dried at 120°C, and then degreased at 550°C in an air atmosphere for 3 hours. Next, the degreased columnar honeycomb structure with the electrode layer forming paste was fired and oxidized to produce a columnar honeycomb structure. The firing was performed in an argon atmosphere at 1450°C for 2 hours. The oxidation was performed in the air at 1300°C for 1 hour.

(6. Preparation of Undercoat Layer Forming Paste)
Metal (SUS430) powder, crystalline glass (MgO-Al ₂ O ₃ -SiO ₂ ) powder, methyl cellulose, glycerin, and water were mixed in a planetary agitator to prepare a base layer forming paste. Here, the metal powder and the glass powder were mixed so that the volume ratio of the metal powder to the glass powder was 40:60. In addition, when the total of the metal powder and the glass powder was 100 parts by mass, the amount of the methyl cellulose was 0.5 parts by mass, the amount of the glycerin was 10 parts by mass, and the amount of the water was 38 parts by mass. The average particle diameter of the metal powder was 10 μm. The average particle diameter of the glass powder was 5 μm. As shown in Table 1, the volume ratio of the metal and the glass changes from the volume ratio at the stage of preparing the base layer forming paste due to aggregation caused by laser irradiation of the base layer described later.

(7. Application of Undercoat Layer Forming Paste)
Next, the base layer forming paste was applied to only the area required for welding the metal terminal so as to partially cover the electrode layer, thereby obtaining a columnar honeycomb structure with the base layer forming paste. At this time, the base layer forming paste was screen printed so that the applied thickness was uniform.

(8. Firing)
Next, the columnar honeycomb structure with the base layer forming paste was dried with hot air at 80°C for 1 hour, and then fired in an argon atmosphere at 1000°C for 2 hours to prevent the crystalline glass from changing into amorphous glass.

The second base layer-attached columnar honeycomb structure obtained under the above manufacturing conditions had a bottom surface that was circular with a diameter of 100 mm and a height (length of the cells in the flow path direction) of 100 mm. The cell density was 93 cells/ ^cm2 , the thickness of the outer peripheral wall was 300 μm, the thickness of the partition walls was 101.6 μm, the porosity of the partition walls was 45%, and the average pore diameter of the partition walls was 8.6 μm. The thickness of the electrode layer was 0.3 mm.

(9. Partial Amorphization of Underlayer (Formation of First Underlayer))
A laser was irradiated toward the outer surface of the base layer of the columnar honeycomb structure with the second base layer obtained under the above manufacturing conditions. At this time, the thickness and oxide composition of the first base layer and the second base layer were changed by changing the laser output, the laser spot diameter, and the laser irradiation time according to the test number. Note that this laser irradiation was not performed in Comparative Example 1.

(10. Welding of metal terminals)
A SUS plate-shaped metal terminal having a thickness of 0.4 mm was placed on the upper surface of the base layer of the columnar honeycomb structure with base layer obtained under the above manufacturing conditions. Then, the plate-shaped metal terminal was irradiated with a laser using a fiber laser welding machine. At this time, the laser output was 200 W/mm ² , the irradiation time was 0.5 seconds, and the laser spot diameter was 4.0 mm. In this way, the SUS plate-shaped metal terminal was welded to the base layer. In Comparative Example 2, the laser irradiation was performed in the same manner as in the other Examples, except that the laser irradiation conditions were changed to a laser output of 150 W/mm ² and an irradiation time of 0.5 seconds, and the SUS plate-shaped metal terminal was welded to the base layer.

(11. Characterization)
The following characteristic evaluations were carried out for the pillar-shaped honeycomb structures with metal terminals obtained under the above manufacturing conditions. Note that the pillar-shaped honeycomb structures with metal terminals were prepared in the number necessary for the following characteristic evaluations.

(a) Oxide composition of the base layer For the columnar honeycomb structure with metal terminals obtained under the above manufacturing conditions, one base layer for each test number was observed by SEM at a magnification of 300 by the above-mentioned method, and the base layer was divided into a first base layer and a second base layer based on the brightness and shading on the SEM image, and the volume ratio of crystalline oxide and amorphous oxide in the oxide in each base layer was obtained. The results are shown in Table 1. Note that the volume ratio of crystalline oxide and amorphous oxide in the oxide by the EBSD method was not measured here, but according to the inventor's experience, it is estimated that the judgment result of whether the crystalline oxide or the amorphous oxide is the main component obtained by the EBSD method will be the same as the result in Table 1.

(b) Thickness of Underlayer For the columnar honeycomb structure with metal terminal obtained under the above manufacturing conditions, the thickness of the first underlayer at the portion in contact with the metal terminal and the thickness of the second underlayer at the portion adjacent to the first underlayer were measured during the above SEM cross-sectional observation. The results are shown in Table 1.

(c) Metal volume concentration For the columnar honeycomb structure with metal terminals obtained under the above manufacturing conditions, the metal volume concentration ( _v1 ) in the first base layer and the metal volume concentration ( _v2 ) in the second base layer were measured based on the brightness in the SEM image during cross-sectional observation using the SEM described above.

(d) Linear expansion coefficient The linear expansion coefficient was measured according to JIS Z2285:2003 when the temperature was changed from 25°C to 1000°C using test pieces made of the same material as the outer wall, electrode layer, first base layer, second base layer, and metal terminal of the columnar honeycomb structure with metal terminal obtained under the above manufacturing conditions. The linear expansion coefficient was 4.2 x ^10-6 /K for each test number for the outer wall, and 11.8 x ^10-6 /K for each test number for the metal terminal. Other results are shown in Table 1. In Table 1, _α1 is the linear expansion coefficient of the first base layer, _α2 is the linear expansion coefficient of the second base layer, and _α3 is the linear expansion coefficient of the electrode layer.

(e) Volume resistivity Using test pieces made of the same material as the outer wall, electrode layer, first base layer and second base layer of the columnar honeycomb structure with metal terminals obtained under the above manufacturing conditions, the volume resistivity (Ω·cm) at 25°C was measured by the four-terminal method. The volume resistivity (Ω·cm) of the outer wall was 0.01 Ω·cm for each test number, and the volume resistivity of the electrode layer was 0.004 Ω·cm for each test number. Other results are shown in Table 1.

(f) Crack Measurement The columnar honeycomb structure with metal terminals obtained under the above manufacturing conditions was examined with a magnifying glass at a magnification of 40 times to see whether cracks occurred in the base layer. The number of base layers examined was 20, and the number of base layers in which cracks were confirmed was counted. The results are shown in Table 1. In Comparative Example 1, since no laser irradiation was performed to form the first base layer, the oxide constituting the base layer was only crystalline. Therefore, cracks occurred at a high rate in the base layer of the obtained columnar honeycomb structure with metal terminals. In Comparative Example 2, since the laser irradiation conditions for forming the first base layer were inappropriate, the metal volume concentration was different from that of the second base layer, and the first base layer in which the crystallinity of the oxide was maintained was formed. On the other hand, in Invention Examples 1 to 5, since the laser irradiation conditions for forming the first base layer were appropriate, the first base layer in which amorphization progressed was formed, and the occurrence of cracks was suppressed.

100, 200 Electrically heated carrier 110 Columnar honeycomb structure 112a Peripheral wall 112b Electrode layer 113 Partition wall 114 Peripheral side surface 115 Cell 116 One end face 118 Other end face 120 Base layer 120a First base layer 120b Second base layer 130 Metal terminal 131 Welded portion 140 Intermediate layer

Claims (14)

An electrically conductive columnar honeycomb structure having an outer peripheral side surface and partition walls disposed inside the outer peripheral side surface and partitioning a plurality of cells forming a flow path from one end surface to the other end surface;
One or more base layers disposed directly or via an intermediate layer on the outer peripheral side surface of the honeycomb structure, and
a metal terminal bonded to the one or more substrate layers;
An electrically heated carrier comprising:
Each base layer is
a first underlayer in contact with the metal terminal, containing a metal and an oxide, the oxide being mainly composed of an amorphous oxide;
a second underlayer adjacent to the first underlayer and in contact with the outer peripheral side surface or the intermediate layer, the second underlayer containing a metal and an oxide, the oxide being mainly composed of a crystalline oxide;
Regarding the linear expansion coefficient measured according to JIS Z2285:2003 when the temperature is changed from 25°C to 1000°C, the linear expansion coefficient of the first underlayer is larger than the linear expansion coefficient of the second underlayer.
Electrically heated carrier. The electrically heated carrier according to claim ₁ , wherein the linear expansion coefficient α1 of the first base layer and the linear expansion coefficient _α2 of the second base layer satisfy the relationship 3.0 ≧ _α1 / _α2 ≧ 1.2 when measured according to JIS Z2285:2003 when the temperature is changed from 25°C to 1000°C. 3. An electrically heated carrier as described in claim ₁ or ₂ , wherein, with respect to the volume resistivity at 25°C measured by a four-terminal method, the volume resistivity _ρ1 of the first underlayer and the volume resistivity _ρ2 of the second underlayer satisfy the relationship 1.0≦ρ1/ρ2≦1.5. The electrically heated carrier according to any one of claims 1 to 3, wherein the first underlayer and the second underlayer both contain one or more metals selected from a Ni-based alloy, an Fe-based alloy, a Ti-based alloy, a Co-based alloy, metallic silicon, and Cr. The electrically heated carrier according to any one of claims 1 to 4, wherein the first underlayer and the second underlayer both contain metals with the same atomic number. An electrically heated carrier according to any one of claims 1 to 5, wherein the first underlayer contains one or more amorphous oxides selected from oxide glass and chalcogenide glass, and the second underlayer contains one or more crystalline oxides selected from oxide glass, Si-based material, and chalcogenide glass. The electrically heated carrier according to any one of claims 1 to 6, wherein the amorphous oxide contained in the first underlayer and the crystalline oxide contained in the second underlayer are both oxides of elements having the same atomic number. An electrically heated carrier according to any one of claims 1 to 7, wherein the volume concentration _v1 (%) of the metal in the first underlayer and the volume concentration _v2 (%) of the metal in the second underlayer satisfy the relationship 0.7≦ _v1 / _v2 ≦1.6. An electrically heated carrier according to any one of claims 1 to 8, wherein the metal terminal has a welded portion that is joined to the base layer. An electrically heated carrier as described in any one of claims 1 to 9, wherein, with respect to the linear expansion coefficient measured according to JIS Z2285:2003 when the temperature is changed from 25°C to 1000°C, the linear expansion coefficient _α2 of the second base layer and the linear expansion coefficient _α3 of the member or intermediate layer constituting the outer side surface with which the second base layer contacts satisfy the relationship 1.0≦ _α2 / _α3 ≦2.0. the first underlayer is composed of an Fe-based alloy and an amorphous oxide glass;
the second underlayer is composed of an Fe-based alloy and a crystalline oxide glass;
The electrically heated carrier according to any one of claims 1 to 10. The honeycomb structure has an outer wall, and an electrode layer disposed on an outer surface of the outer wall and having a volume resistivity lower than that of the outer wall, and a part of the outer peripheral side surface is constituted by the electrode layer,
The one or more underlayers are disposed on the electrode layer directly or via an intermediate layer.
An electrically heated carrier according to any one of claims 1 to 11. An electrically heated carrier according to any one of claims 1 to 12, wherein the one or more underlayers are disposed on the outer peripheral side surface via an intermediate layer, and the intermediate layer contains an amorphous silicon compound. An electrically heated carrier according to any one of claims 1 to 13;
and a cylindrical metal tube that houses the electrically heated carrier.